Is there anything out there that isn't the $2 one that has a ton of limits such as the first FAT file you write becomes file #1 and so on? Would be nice if it could play multiple MP3 files at the same time as well.

Now this is much more like what we had in mind. Even supports polyphonic outputs.

Supporting up to 2048 uncompressed 16-bit, 44.1kHz wav files – the same quality as an audio CD – the WAV Trigger can play and mix up to 14 stereo tracks simultaneously and independently, with very low latency. Tracks can be controlled via 16 programmable trigger inputs, or by using a native serial control protocol or even MIDI.

Trigger inputs can be connected directly to switches and buttons, or to digital outputs from sensors or another microcontroller. Alternate functions can be specified using a free cross-platform GUI application, and allow triggers to play sequential or random tracks, pause and resume groups of tracks and even control volume. An Arduino library allows for complex serial control like real-time mixing, starting multiple tracks in sample-sync and smooth cross-fading between tracks.

The higher end version also supports Python, which is nice. I know it's a competing product but I looked around for a good while through Adafruit and elsewhere before finally coming across these and just wanted to share.

Oddly enough, the pricing for the first one I linked that was built 9 years ago is the same price, which is higher than the ones that I linked above that are much more modern.